🧪 CBSE · Class 12 · Chemistry · Chapter 2

Chapter 2:
Solutions

Complete chapter resources for CBSE Class 12 Chemistry — concentration terms, Raoult's law, colligative properties, van't Hoff factor, and instant AI question paper generation.

4Topics
5–7Board marks
8Sample questions
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Key Formulas — Chapter 2
  • Raoult's law: p₁ = p₁° × x₁
  • Boiling point elevation: ΔTb = Kb × m
  • Freezing point depression: ΔTf = Kf × m
  • Osmotic pressure: π = iMRT
  • Henry's law: p = KH × x
  • van't Hoff factor: i = 1 + α(n − 1)
Chapter Overview

What this chapter covers

A solution is a homogeneous mixture of two or more pure substances. Chapter 2 begins by classifying solutions by phase and by the relative amounts of solute and solvent, then establishes the key concentration terms — mole fraction, molality, molarity, and mass percentage — that are used throughout the chapter and in subsequent chapters of physical chemistry.

The chapter develops Raoult's law for the vapour pressure of solutions and uses it to distinguish ideal from non-ideal behaviour. Henry's law for the solubility of gases in liquids is treated alongside Raoult's law as a limiting case. Together these laws underpin the four colligative properties: relative lowering of vapour pressure, elevation of boiling point, depression of freezing point, and osmotic pressure — all of which depend only on the number of solute particles, not their identity.

For electrolytic solutes, the van't Hoff factor (i) corrects colligative property calculations by accounting for dissociation (i > 1) or association (i < 1). Board problems typically ask students to calculate molar mass of a solute from a measured colligative property, or to determine the degree of dissociation of an electrolyte — making this chapter heavily numerical and formula-driven.

Topics

What's inside Chapter 2

As per NCERT Class 12 Chemistry Part I (CBSE syllabus)

Topic 1
Types of Solutions & Concentration Terms
Classification of solutions by phase. Expressing concentration as mass %, mole fraction, molarity (M), molality (m), and parts per million. Interconversion of concentration units.
Topic 2
Vapour Pressure & Raoult's Law
Vapour pressure of liquid solutions. Raoult's law for volatile and non-volatile solutes. Ideal and non-ideal solutions. Positive and negative deviations from Raoult's law. Azeotropes.
Topic 3
Colligative Properties
Relative lowering of vapour pressure. Elevation of boiling point (ΔTb = Kb × m). Depression of freezing point (ΔTf = Kf × m). Osmosis and osmotic pressure (π = MRT). Reverse osmosis.
Topic 4
Abnormal Molar Masses & van't Hoff Factor
Dissociation and association of solutes. van't Hoff factor i = observed colligative property / calculated colligative property. Modified colligative property equations. Degree of dissociation/association.
Connections

How this chapter fits in

Useful for setting question difficulty and cross-chapter papers.

Builds on
Ch 1 · The Solid State
Intermolecular forces; lattice energy concepts carry into solution behaviour
Class 11 · Some Basic Concepts of Chemistry
Mole concept, molarity, and stoichiometry used throughout concentration calculations
Chapter 2 Solutions
Leads to
Ch 3 · Electrochemistry
Electrolytic solutions; ionic strength; conductance in solution
Ch 4 · Chemical Kinetics
Rate laws expressed in molarity; concentration–rate relationships
Board Blueprint

Marks & question-type breakdown

Typical pattern based on CBSE Class 12 Chemistry board papers from the last five years.

Question type Marks Typical count What's usually tested
MCQ / Assertion–Reason 1 1–2 Identifying ideal solutions, Henry's law application, or nature of deviation
Very Short Answer 2 1 Define/state Raoult's law, Henry's law, or calculate a concentration term
Short Answer 3 1 Numerical on boiling point elevation or freezing point depression; van't Hoff factor
Long Answer / Numerical 5 1 Osmotic pressure problem, molar mass determination, or multi-step colligative calculation
Total (approximate) 5–7 3–4 Weightage varies across paper sets and years
Sample Questions

8 sample questions — generated by MarksZen AI

Aligned to CBSE Class 12 Chemistry Chapter 2. Covers all question types across Easy, Medium, and Hard difficulty.

Q1 Easy 1 mark MCQ
Which of the following concentration terms is independent of temperature? (a) Molarity (b) Normality (c) Molality (d) Mole fraction in terms of volume
Q2 Easy 2 marks Short Answer
State Henry's law. Give one application of Henry's law from everyday life.
Q3 Medium 2 marks Short Answer
18 g of glucose (C₆H₁₂O₆, M = 180 g/mol) is dissolved in 1 kg of water. Calculate the molality of the solution. (Given: M of water = 18 g/mol)
Q4 Medium 3 marks Short Answer
The vapour pressure of pure benzene at 25 °C is 640 mm Hg. When 2.0 g of a non-volatile solute is dissolved in 78 g of benzene, the vapour pressure falls to 600 mm Hg. Calculate the molar mass of the solute. (M of benzene = 78 g/mol)
Q5 Medium 3 marks Word Problem
An aqueous solution of urea (M = 60 g/mol) freezes at −0.372 °C. Calculate the molality of the solution and the amount of urea present per litre of the solution. (Kf of water = 1.86 K kg mol⁻¹; assume density of solution = 1 g/mL)
Q6 Hard 4 marks Word Problem
A 0.2 molal aqueous solution of KCl shows a freezing point depression of 0.68 °C. Calculate the van't Hoff factor for this solution and the degree of dissociation of KCl. (Kf for water = 1.86 K kg mol⁻¹)
Q7 Hard 5 marks Word Problem
A solution is prepared by dissolving 10 g of a non-electrolyte solute in 200 g of water. The solution boils at 100.52 °C. Calculate: (i) The molality of the solution. (ii) The molar mass of the solute. (iii) The osmotic pressure of the solution at 27 °C if its density is 1.02 g/mL. (Kb for water = 0.52 K kg mol⁻¹; R = 0.082 L atm mol⁻¹ K⁻¹)
Q8 Hard 5 marks Case-Based
Benzene and toluene form an ideal solution. At 40 °C the vapour pressure of pure benzene is 160 mm Hg and that of pure toluene is 60 mm Hg. A solution is made by mixing 2 mol benzene with 3 mol toluene. (i) Calculate the mole fractions of benzene and toluene in the solution. (ii) Calculate the partial vapour pressure of each component. (iii) Calculate the total vapour pressure of the solution. (iv) Find the mole fraction of benzene in the vapour phase.
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Previous Year Questions

From CBSE board examinations

Actual questions from past Class 12 Chemistry board papers — Solutions chapter.

Board 20223 marks
A solution of glycerol (C₃H₈O₃) in water was prepared by dissolving some glycerol in 500 g of water. This solution has a boiling point of 100.42 °C. What mass of glycerol was dissolved to make this solution? (Kb for water = 0.512 K kg mol⁻¹) (CBSE All India 2022)
Board 20232 marks
Define the term 'osmotic pressure'. How is it related to the molar concentration of the solution? Write the relationship and identify each term. (CBSE Delhi 2023)
Board 20203 marks
A 0.5 g sample of a polymer was dissolved in 100 mL of water. The osmotic pressure of this solution at 27 °C was found to be 2.46 × 10⁻³ atm. Calculate the molar mass of the polymer. (R = 0.082 L atm mol⁻¹ K⁻¹) (CBSE 2020)
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FAQ

Questions teachers ask

How many marks does Solutions carry in the CBSE Class 12 Chemistry board exam? +
Typically 5–7 marks across 2–3 questions — one 2-mark short answer on concentration terms or Henry's law, and one 3–5 mark question on colligative properties or Raoult's law. This chapter has featured in CBSE Class 12 Chemistry board papers consistently over the past several years.
What is Raoult's law and how is it tested in board exams? +
Raoult's law states that the partial vapour pressure of a solvent above a solution is equal to the vapour pressure of the pure solvent multiplied by the mole fraction of the solvent: p₁ = p₁° × x₁. Board questions typically involve calculating partial pressure of components, total vapour pressure of a mixture, or identifying ideal vs. non-ideal solutions. These appear as 2–3 mark questions almost every year.
Which colligative properties are most important for CBSE Class 12 board exams? +
All four colligative properties — relative lowering of vapour pressure, elevation of boiling point, depression of freezing point, and osmotic pressure — are important. Depression of freezing point (ΔTf = Kf × m) and osmotic pressure (π = iMRT) are the most frequently tested in long-answer questions because they involve numerical problem-solving. Elevation of boiling point and van't Hoff factor 'i' also appear regularly as 2-mark questions.
What is the van't Hoff factor and when does it matter? +
The van't Hoff factor (i) accounts for the association or dissociation of solute particles in solution. For electrolytes that dissociate (like NaCl → 2 ions), i > 1, making colligative effects larger. For solutes that associate (like acetic acid in benzene forming dimers), i < 1. Board questions often ask students to calculate the degree of dissociation or association from a given colligative property value using the formula i = 1 + α(n − 1) for dissociation.
How do I generate a custom question paper for Solutions (Class 12 Chemistry) using MarksZen? +
Sign up for a free MarksZen account, choose CBSE Class 12 Chemistry, select Chapter 2 (Solutions), set your preferred question-type mix and total marks — the AI generates a complete board-aligned paper with answer key in under 2 minutes, ready for PDF export.